What are some interesting plot ideas for a Harry Potter Riddick crossover fanfiction?

One interesting idea could be the exploration of a unique friendship between characters from Harry Potter and Riddick universes. For example, how Harry's magic might interact with Riddick's survival skills in a dangerous situation. Another could be the creation of a new magical - like world that combines elements of both, like a prison in the wizarding world where Riddick - like characters are held.

A plot could involve Ciel Phantomhive being magically transported to Hogwarts. Since he's used to a world of mystery and intrigue in his own story, he might quickly adapt to the secrets of Hogwarts. He could form an unlikely alliance with Harry Potter and his friends, and together they face a new threat that combines elements from both universes, like a dark wizard who has made a deal with a demon.

Perhaps the wizards from Harry Potter could teach the Avengers some magic. For example, Harry could show them how to use the Patronus charm for protection. In return, the Avengers could introduce the wizards to their high - tech gadgets. Iron Man could be especially interested in the magical properties of things like the Elder Wand. And then there could be a big battle where the combined powers of magic and technology are used to fight off a new, powerful enemy.

One idea could be that Harry Potter and his friends accidentally end up in the world of My Little Pony. They could learn about the magic of friendship in Equestria, which is different from the magic they know in the wizarding world. Maybe they help the ponies fight a dark force using their unique spells.

One idea could be that the vampires in Twilight are discovered by the wizarding world in Harry Potter. The wizards might be intrigued and cautious at the same time. They could study the vampires' immortality and special abilities, while the vampires might be interested in the magic that wizards possess.

In a crossover, Merida could teach the Hogwarts students about her own form of magic, like the spells she uses for her archery and how she communicates with the animals in her world. At the same time, she could learn about the complex spells and potions of the wizarding world. This exchange of knowledge could lead to some exciting adventures, like using a combination of both types of magic to defeat a common enemy.

One idea could be that the Hogwarts students discover Halo technology. Maybe Harry and his friends find a crashed UNSC ship and start to study its advanced weaponry and shields. They could try to adapt the technology to defend Hogwarts from Voldemort. Another plot could involve Master Chief being sent to the wizarding world by accident. He then has to navigate the strange new world of magic while also dealing with threats that his usual Halo combat skills might not be fully equipped for.

Another plot could involve a time - travel crossover. Cedric somehow travels back in time and meets a younger Harry. They work together to change certain events that would have led to Cedric's death in the original timeline. This could also involve Cedric teaching Harry some of the Hufflepuff values and spells that he might not have known before.

One idea could be that Buffy is transported to the wizarding world. She could use her slayer skills to fight dark wizards. Maybe she teams up with Harry Potter to take on a new kind of threat that combines the powers of vampires and dark magic.

In a crossover fanfiction, the Sorting Hat could end up on Pandora. The Na'vi are confused by this strange object. One of the Na'vi tries it on and it sorts the Na'vi into Hogwarts houses based on their characteristics. This could lead to some Na'vi being selected to study at Hogwarts, and they bring their own unique skills and knowledge of Pandora's magic, which causes quite a stir among the students and faculty at Hogwarts.